Liquid crystal display elements have found wide application due to excellent characteristics such as activation at a low voltage and display on thin devices. Conventional modes for displaying liquid crystal display elements include TN (twisted nematic), STN (super-twisted nematic) and TN-based active matrix (TFT: thin film transistor), all of which have utilized a liquid crystal composition having a positive dielectric constant anisotropy. However, one disadvantage of these display modes is a narrow viewing angle, which is a major problem to be improved in association with an ever increasing demand for larger display panels.
In recent years, as a countermeasure for solving this problem, display modes such as vertical alignment mode and IPS (in-plane switching) have newly come into practical use. The vertical alignment mode is a mode in which vertically-aligned liquid crystal molecules are used to improve a view angle and a liquid crystal composition having a negative dielectric constant anisotropy is used. Further, the IPS is a method in which a transverse electrical field facing horizontally to a glass substrate is used to switch liquid crystal molecules, thereby improving the view angle. In this method, a liquid crystal composition having a positive or negative dielectric constant anisotropy is used. As described above, the vertical alignment mode and the IPS, which are effective in improving the view angle, require a liquid crystal compound negative in dielectric constant anisotropy and a liquid crystal composition. Such a requirement is demanded more strongly than ever before. Conventionally, liquid crystal compositions negative in dielectric constant anisotropy substantially include compounds having 2,3-difluorophenylene groups (Patent Document 1). However, liquid crystal compositions which use these compounds are not sufficiently great in the absolute value of dielectric constant anisotropy, which is a problem (Patent Document 2).
Compounds negative in dielectric constant anisotropy and having a large absolute value include a trifluoronaphthalene derivative, and many other compounds have already been disclosed in general (Patent Document 3). However, producing compounds having a trifluoronaphthalene skeleton is not necessarily easy, and it is not recognized that the compounds are disclosed in the above-described reference documents. Further, in the reference documents, such consideration is given that the compounds are used in a ferroelectric liquid crystal composition. No disclosure is found concerning which compound in such a widely disclosed scope as a nematic liquid crystal composition negative in dielectric constant anisotropy is used in a specific manner, which compound is used together, or what effect is obtained thereby.
On the other hand, a trifluoronaphthalene-based compound and a liquid crystal composition which contains the compound have been known. However, there is no disclosure about a liquid crystal composition in which a compound having a cyclohexylmethoxy group at the 6-position of a naphthalene ring is used (refer to Patent Documents 4, 5 and 6).
Further, based on a finding that compounds having an alkoxy group at the 2-position of a benzene ring and a cyclohexylmethoxy group at the 6-position are chemically unstable and therefore not usable, it has been considered that compounds having an alkoxy group at the 2-position of a naphthalene ring and a cyclohexylmethoxy group at the 6-position thereof are also chemically unstable and not usable as a liquid crystal material. Therefore, the compound concerned was not developed as a liquid crystal material (Non-patent Document 1).
[Patent Document 1]
Japanese Translation of International Application (Kohyo) No. H2-503441 (example on page 8)
[Patent Document 2]
Japanese Published Unexamined Patent Application No. H10-176167 (example on page 10)
[Patent Document 3]
German Patent Application No. 19522195 (manufacturing method on page 12)
[Patent Document 4]
Japanese Published Unexamined Patent Application No. 2001-40354
[Patent Document 5]
Japanese Published Unexamined Patent Application No. 2004-250668
[Patent Document 6]
Japanese Published Unexamined Patent Application No. 2004-204133
[Non-patent Document 1]
Numata, “Trend of liquid crystal materials,” Monthly DISPLAY, Vol. 4, No. 3 (page 5), March 1998